im so sorry but the whole novel is so much for me to spoil m(_ _;)m
but i will give you the novel link just.. you know make sure to study... heheh... although im the same as you as i cant stop myself from binge reading once i start (;・∀・)
https://www.novelupdates.com/series/my-fiance-is-in-love-with-my-little-sister/
although just so you know... it seems like the author still didnt finish the novel yet but the latest chapter can already be consider as the epiloge
Here's some spoiler:
http://www.mangago.zone/home/mangatopic/6952805/
i promise myself that i will not experience this story once again after i binge read the whole novel a year ago.... and here they adapt it into a manga that o so much tempted to read but Nayyyy i will not shed tears again (/TДT)/